Remove dependency on eigenbase-resgen

Details

Description

Eigenbase-resgen generates classes for type-safe access to resources such as error messages. This is good. But it those generated classes use classes from a runtime library, and that requires eigenbase-resgen.jar to be on the runtime path.

Only a couple of classes are used (ShadowResourceBundle and ResourceDefinition, both in the org.eigenbase.resgen package). It may be possible to replace those classes with generated or hand-written classes, and therefore remove eigenbase-resgen.jar from the runtime classpath. It would continue to be used at build-time, to generate the classes.